Green has too much blue in it; it's more 'alerting' than the yellow/orange/red of f.lux. Yellows, oranges and reds are best for humans at night while blues and greens and whatnot are best for us during the day.

The research shows that with green light the sleep afterwards is faster and deeper ?

They were studying mice. Do the same test with humans, and I'm sure you'll find green light to be more alerting than yellow, orange and red because the body responds to blue light (which is very present in green light) by producing a more alert and awake feeling. Remove all blue light for an hour or two and the body responds by producing melatonin. Once enough melatonin is produced, the body begins producing other things that make it easy to fall asleep.

So, green light is more alerting than yellows oranges and reds because it has much more blue light. You don't want to be exposed to any blue light when you want your body to be producing melatonin.

Nocturnal means you're active mainly at night, and diurnal means you're active mainly during the day. I think it helps to think of "N" for "Night" and "D" for "Day". This means that nocturnal creatures are the opposite to human beings in terms of what colors of light affect us and how those colors effect us. Their day is our night, and their night is our day.

I left the following comment on that article:

The title is misleading and the summary at the beginning is a major misunderstanding:

"A team of researchers from Oxford University have been able to show that different colors of light affect our ability to sleep as well as the level of our alertness."

The results of this study can't apply to us because mice are nocturnal and we are diurnal. This means that mice are mostly active at night and that we are mostly active during the day. It means that a sunrise and daylight affects mice in the same way a sunset and the lack of light at night affects us. It means that their day is our night, and their night is our day. Therefore, the colors of light that make them alert and the colors that make them sleepy are the opposite from the colors of light that make us alert or sleepy. In other words, the results of this study were never intended to be applied to us humans.

Green light has a lot of blue in it, and blue light is very "alerting" for us. It tells our body that it's daytime and that it's time to be active and alert. Exposure to blue light prevents the human body from producing melatonin (and it makes the body stop producing it if it's currently producing it). The amount of blue light in sunlight gradually gets lower and lower as the sun gets closer and closer to the horizon (starting at around midday). Due to our planet's rotation, we are physically moving away from the sun, albeit very slowly - thus creating the light effect known as Redshift. During a sunrise, we experience Blueshift because we are physically moving towards the sun.

So, the colors seen during a sunset are always very warm (we see yellows, oranges and reds). This is why we begin to feel relaxed and even sleepy because the body is beginning to produce melatonin, and the increase of melatonin in the body triggers other chemicals to be produced that cause us to become relaxed and sleepy. There's much more blue light during a sunrise, and that's why a sunrise is energizing and can make you feel more awake and alert even if you've stayed awake all night. Blue light makes the body produce chemicals that get us going and keep us going.

There's already a huge amount of research on the way blue light affects us, and the findings of that research are the exact opposite to what these researchers found in their mice. Again, mice are nocturnal and we are diurnal, so the results of this study cannot be applied to us. I would even go as far as saying that someone just assumed their reason for conducting this study was to see how light affects us simply because mice are commonly used as study subjects instead of humans. So obviously, just because experiments are being performed on mice, it doesn't mean they're conducting those experiments in order to learn more about ourselves. Sometimes you just want to know more about an animal, particularly a nocturnal animal in this case, and that's all they were doing here.

Mice have a more immediate reaction to bright light: they fall asleep! However, in this study they found blue light so stressful, they would run away and seek darkness instead.

If I remember correctly, people are likely to have a similar reaction for arousal, but the opposite one for circadian impact (because we're diurnal, not nocturnal), which makes the systems somewhat different.

Here is a recent study in humans that shows more alerting affects due to 460nm than 555nm light: blue light is still alerting during the day, but has stronger circadian effects at night: